1. Your Friends Have More Friends Than You Do: Identifying Influential Mobile Users Through Random Walks Bo Han, Aravind Srinivasan University of Maryland MobiHoc ‘12 Presented by YongJoon Chung

2. Contents  Introduction  iWander  Controlling Infectious Diseases  Facilitating Information Dissemination  Conclusion 2

3. Introduction  Identifying influential users in mobile social networks.  Previous methods uses centralized algorithms on either friendship or social-contact graphs of all users High computational complexity  Proposes iWander, a lightweight and distributed protocol Extremely low message overhead 3

4. iWander - Intuition  If a small group of smartphones initialize random walks periodicaaly, influential mobile users may be visited by these random walks more frequently than average. 4

5. iWander - Protocol  Every ΔT hours, iWander generates probing message with a given probability q on each smartphone. Message only contains a pre-configured time-to-live (TTL) filed L.  When a smartphone receives a probing message, it decreases L by 1, stores it in its local queue, and passes the queued message when different peer is in contact. When L is 0, iWander discards the message.  iWander maintains a random-walk counter The higher the counter gets, the more influential the user is. 5

6. iWander - Protocol 6 1. Every ΔT hours, senses nearby device 2. With probability q, send length T random-walk message T = 2 Random walk count +1 Queue T = 1

7. Controlling Infectious Diseases  iWander can be used to control infectious diseases and perform early outbreak detection. Vaccinating people with high random-walk counters first can help to contain spread of flu. 7

8. Controlling Infectious Diseases  Simulation setup C based simulator on the SIR model for spread of infectious diseases simulation. Used Dartmouth dataset for individual social contact simulation.  Dartmouth dataset – records of association and disassociation events at WiFi access points Comparison with random immunization. 8

9. Controlling Infectious Diseases 9

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11. Facilitating Information Dissemination  iWander can be used for target-set selection of information dissemination Can be used for opportunistic communications and social participation to facilitate information dissemination Use iWander to select target users without requiring global network structure Top k random-walk counters will receive data from server and disseminate to other users. 11

12. Facilitating Information Dissemination  Simulation setup C based simulator with the same Dartmouth data set for performance evaluation of random-walk based target-set selection Compare the performance with random selection. Also compare with hybrid method which uses 10% from 1-set random walks and 90% from low centrality. 12

13. Facilitating Information Dissemination 13

14. Facilitating Information Dissemination 14

15. Conclusion  The paper proposed a light weight and distributed protocol for identifying influential mobile users who have high centrality in their social-contact networks.  iWander was evaluated for two applications and outperformed the random approach. 15

16. Thank you! 16